Technical Field
The present invention relates to a method of exciting photosensitive materials and, more particularly, to a method of exciting photosensitive substances in producing therapeutic effects by causing the photochemical substances to accumulate on or in various cancer cells or cancer tissues, or abnormal cells or abnormal tissues and exciting the photosensitive substances that have accumulated, to thereby kill or damage the cancer cells, cancer tissues and so on.
The use of photosensitive substances for selectively killing or damaging various cancer cells or cancer tissues is known. The photosensitive substances accumulate on or in various cancer cells or cancer tissues, or abnormal cells or abnormal tissues and then, upon excitation generally with visible rays such as laser beams, they undergo chemical reactions and kill or damage various cancer cells or cancer tissues more specifically than normal tissues to thereby produce therapeutic effects.
On the occasion of treatment, a photosensitive substance is systemically administered and then the photosensitive substance is excited endoscopically with laser beams in the case of cancer or carcinoma of the stomach, esophagus, lung, larynx and pharynx, uterine cervix, bladder or the like, or directly with laser beams in the case of cancer or carcinoma on the body surface, for example skin cancer.
When, according to the prior art, light is used as the energy source for excitation, the range of killing and damaging effects or therapeutic effects depends on the extent of tissue penetration of visible rays such as laser beams, and the maximum penetration is said to be about 1.5 cm. Therefore, the effects can be produced only on superficial lesions, in particular early carcinomas, and the range of application is restricted.
Excitation with light is effective only against localized lesions and is quite incapable of bringing about complete recovery in patients with metastatic cancer.
In the case of excitation with light, a long period of irradiation, generally scores of minutes, is required for attaining satisfactory effects.
In the case of using a photosensitive substance for removing cancer cells in blood by extracorporeal circulation or for removing minute cancer cells remaining in autologous bone marrow transplants (purging), the use of light for excitation can hardly result in successful excitation since the light is blocked by erythrocytes contained therein.
Under the existing circumstances, as mentioned above, light irradiation has its limits against cancer cells in the depth of tissues, which light cannot reach, or in blood, and its range of application is limited to those sites which involve superficial lesions that can be confirmed visually and can be irradiated with light. Another problem is that a long period of time is generally required for light irradiation.
On the other hand, irradiation with ultrasonic waves in lieu of light has been proposed, as described in Uchida et al. "Effects of acoustochemical therapy using porfimor sodium on adult T cell leukemia cells", Jpn Med Ultrasonic, Vol. 23, No. 9 (1996), pp. 23-28.
However, the excitation with ultrasonic waves has the following problems.
Since ultrasonic waves are very poor in propagation efficiency in the air, it is difficult to apply them to digestive tracts, lungs and the like, which have lumina or cavities. Further, since ultrasonic waves are to be used in contact with the target, it is difficult to irradiate a wide range, for example over the whole body, therewith. In addition, since ultrasonic waves can hardly permeate bone portions, it is difficult to irradiate the inside of bones therewith.
Accordingly, it is an object of the present invention to efficiently excite photochemical substances against cancer lesions in the depth of tissues, which are unaccessible by light or ultrasonic waves, or against cancer cells in blood.